Middle to late Holocene sea surface temperature and productivity changes in the Northeast Pacific

Abstract:

Sea surface temperature (SST) variations in the Northeast Pacific affect regional climate, marine ecosystems, and the society. Previous studies have suggested spatiotemporal shifts in marine habitat, primary productivity, and trophic dynamics in this region in response to radiative forcing. However, these studies rely on models that contain uncertain temperature trends and ecosystem trophic dynamics. Thus, the effects of forced SST change on marine ecosystems in this region remain elusive.

Analysis of SST and plankton productivity proxy records jointly with climate model simulations provides an alternative to (1) quantify observed SST and productivity change, (2) evaluate models’ ability to simulate long term SST changes, (3) identify the dynamics and forcing behind observed changes, and (4) infer the reliability of future projection studies. The Holocene is a good window to address these questions because the external forcing change is well known, multiple well-dated high resolution sediment cores are available for reconstruction, and a transient simulation with a fully coupled model has been done over this period.

In this study, we present three new alkenone based SST and productivity records from Soledad Basin, Santa Barbara Basin and Saanich Inlet that spans 8000 years (9 – 1 ka BP) and compare these records with two published records off Oregon and Alaska and TRACE21 simulation. We found an initial decrease and then an increase in SST in proxy records, with the largest magnitude observed in high latitude and almost no change in the low latitude. However, these changes are not observed in TRACE21 over the same spatiotemporal window, indicating potential incorrect or missing processes in the model. Nonetheless, heat budget analysis suggests processes that drive SST changes along the Northeast Pacific are regionally dependent. Linearity test on heat budget terms also suggests potential nonlinearity present in the Northeast Pacific. Lastly, we compare SST with productivity proxy records to identify systematic (or lack thereof) covarying changes in the Northeast Pacific. These results will have implications on understanding SST and productivity relationship, fidelity of climate models, detecting and attributing SST and ecosystem changes, and robustness of ecosystem changes in projection studies.